Please do problem no.4 of the attached file.
The Sun is powered by nuclear fusion. In this process protons fuse into helium nuclei. This process is explained step by step on this webpage:
In short, there are four processes involved:
1) Two protons interact via the Weak Interaction to form a deuterium nucleus, a positron and a neutrino.
2) Positrons annihilate when they interact with electrons, giving rise to photons.
3) Protons collide ...
A detailed explanation is given.